An ion milling apparatus which is an aspect of a charged particle beam apparatus including a vacuum container is an apparatus in which a sample is arranged in an evacuated sample chamber, an argon ion beam energized to approximately 10 kV or less is irradiated to the sample, atoms are sprung out from the sample surface utilizing the physical sputtering phenomenon, and milling the sample under a stress-free state. The ion milling apparatus is used in preparing a sample for a scanning electron microscope for example.
The irradiation condition of the ion beam in preparing a sample for a scanning electron microscope is approximately 10 kV for the acceleration voltage and approximately 200 μA for the ion beam current for example. Under such condition, the calorie imparted to the sample by ion beam irradiation becomes approximately 2 J/s. In the ion milling apparatus, the ion beam irradiation range may exceed approximately φ5 mm and the milling time may exceed several hours. In a case of a sample with low melting point such as a polymer material and the like, because the temperature rise in milling for long hours is not negligible, cooling of the sample is required.
In Non Patent Literature 1, a cooling mechanism in which liquid nitrogen and a Peltier element for cooling a sample are used in a vacuum sample chamber is disclosed, and a cooling method in which a liquid nitrogen Dewar arranged outside the sample chamber and a sample stage are connected to each other using a copper braided wire and the like and a cooling method in which the liquid nitrogen Dewar and the sample stage are connected to each other by piping and are used as a coolant, are described.
In Patent Literature 1, an ion milling apparatus is disclosed in which a cooling gas passage is arranged in a substrate holder, and a milling object sample is cooled.